Luminaires have long been used in the entertainment area and other fields to produce dramatic lighting effects on a subject matter. In the theatrical field, many types of luminaires are utilized to provide a variety of effects on the actors, musicians, scenery, etc. For example, spot luminaires are employed to produce a bright and intense beam of light with a finely defined peripheral edge. Wash luminaries are utilized to produce a soft and ill-defined beam of light for flooding a general area, such as the background of a stage. Literally hundreds of such lights are utilized in large performances, such as rock concerts. U.S. Pat. No. 4,392,187 illustrates a highly sophisticated and computerized lighting system well adapted for providing many types of lighting effects.
The trend in developing high performance luminaires is toward microprocessor controlled units having motorized apparatus for altering the properties of the light. Such units include lenses, color changers, dowsers, dimmers, diffusers, as well as power supplies and mechanical apparatus for providing pan and tilt orientations to the luminaire. Owing to the number of components required to produce the various lighting effects, the size and weight of sophisticated luminaires tends to increase. The apparatus for altering the properties of a light beam often include mechanisms for inserting and removing glass panels from the path of the light to create the desired effect. For example, colored panels, such as those disclosed in the patent noted above, as well as in U.S. Pat. No. 4,037,097, are used with step-motors for rotating the color panels in a beam of light to change the hue and saturation properties of the light. Also shown in U.S. Pat. No. 4,392,187, are individual panels which can be pivotally mounted to operate as shutters within the path of the light to thereby produce a desired color. In addition, such panels have been constructed of a textured glass to produce a diffused light beam.
In the stage performance field, it is also required to often produce a diffuse light beam, such as by the noted wash luminaires to illuminate a broad area. A Fresnel luminaire can product such an effect, using lenses with highly textured surfaces to produce the diffuse light. However, the amount of diffusion of the light is difficult to adjust and is usually provided by manual adjustable apparatus. It can be appreciated that such a manual adjustment is often difficult, especially when such a lamp is mounted to an overhead truss frame. Also, other types of light diffusing apparatus are available, but either requires a substantial amount of space in the luminaire housing, is heavy and bulky, or remains within the path of light even if deactivated, or is degraded over time by the light beam. Techniques often used in the art involve the hinging or swinging of a light altering panel of glass into the path of light, and then out of the path when not used. This approach is effective to produce the intended purpose, but requires substantial space to allow the full arcuate swing of the panel.
The color-changing mechanism shown in U.S. Pat. No. 4,602,321 has been used effectively in the VL3 wash luminaire made by Vari-Lite, Inc. of Dallas, Texas, and has been adapted to carry panels of textured, translucent glass which pivot within the path of a light beam and thereby diffuse the beam. It has been discovered by experience that the variable diffuser utilizing pivotable glass panels works best only at the two extremes of travel: fully open or fully closed. This is due to several factors, one of which is that only one type of glass is used in all three panels, yielding three diffuse blobs growing within a field of intense light as the panels are rotated. White light escaping between the partially rotated panels, while quite effective in reducing saturation of a colored beam in a color changer, creates a noticeable pattern of light when used in a pivoting glass diffuser. Once the panels are rotated far enough to completely overlap the entire beam, the diffusion effect almost reaches its maximum level. Further rotation produces only minimal additional diffusion.
It can be seen from the foregoing that a need exists for an improved light altering mechanism which is lightweight, requires little space, and which can be moved entirely out of the path of the beam of light. A further need exists for a mechanism which can be employed in luminaires for moving light altering panels to varying locations within the path of the light to achieve a desired effect, and then move such panels entirely from the light path, into an area in the housing which is normally not used.